Since electric motor was invented centuries ago, development and progress have been made constantly that bring great benefits to people's life. Originally, the electric motor was made in a large size for industrial purpose. Nowadays, numerous smaller electric motors are being made and used on household appliances and machine tools.
The conventional machine tools now being commonly used, such as grinder is driven by a motor for operation. During operation, dust is easily generated that affects working pieces or environment cleaning. To remedy this problem, many machine tools now on the market are equipped with a dust collection device to clear the dust generated during operation of the machine tools. For instance, R.O.C. patent No. M245007 discloses an air discharge apparatus for pneumatic grinders. It mainly includes a body with an upper extension portion and a lower extension portion juxtaposed on the circumference in an up and down manner. The upper extension portion has an air intake vent holding an air intake duct. The lower extension portion has a dust collection hood on a lower side with an opening and a grinding disk located in the opening. The grinding disk has dust suction vents. The lower extension portion further has one side coupled with a dust collection hose connected to a dust collection pouch. When the air intake duct introduces air to drive the grinder, the dust generated during grinding operation can be sucked through the dust suction vents and dust collection hood to enter the lower extension portion, then are introduced through the dust collection hose to enter the dust collection pouch coupled with the distal end of the dust collection hose.
R.O.C. patent No. 517618 also discloses an air discharge structure for pneumatic grinders that includes a grinding wheel equipped with dust suction vents and a dust cover on an upper end of the grinding wheel. The dust cover is fastened to a motor casing. The motor casing holds a pneumatic motor set equipped with a movable blade, and also has an air intake duct and an air expelled duct that are adjacent to each other and integrally extended from one side of the motor casing. The air intake duct and air expelled duct hold respectively an air intake valve set and an air discharge muffler set. The air intake duct and air expelled duct also have respectively a housing chamber to hold a throttle valve and a regulation knob, and two wings integrally extended from the top surfaces to hold a movable air intake trigger. The dust cover has a housing trough holding an air discharge duct pivotally connected to the motor casing. The housing trough is extended to a connection tube of the dust cover. The air discharge duct has an L-shaped duct with a flow guiding plate at a lower end. The air generated by the pneumatic motor can be discharged upwards through an air outlet. The duct has a lower end extended close to a front end of an outlet of the connection tube of the dust cover. Air discharge of the motor and outlet of the connection tube of the dust cover are converged. Dust generated during grinding can be quickly sucked by powerful discharged airflow. The regulation knob is located at the joint of the air discharge duct of the motor casing and air expelled duct and has an engraved portion and a wall portion to control air discharge route to selectively discharge the air through the air expelled duct or air discharge duct.
The aforesaid machine tools respectively clear dust through a dust collection duct installed at one side of the machine tool that collects the dust while the machine tool is in operation. However, dust generated during operation is introduced upwards into the machine tool through the grinding disk and dust collection hood, then enter the dust collection duct by the airflow direction of dust suction. As the dust advancing route is not a closed passage, the dust entered into the machine tool upward cannot be fully sucked into the dust collection duct. Moreover, the motor and cylinder of the machine tool also generate airflow during operation, thus the dust entered into the machine tool upward is easily accumulated in various crevices of the grinder or even inside the cylinder which drives the grinding disk to spin at high speeds. All these could cause damage of the elements of the machine tool.